Heat pump defrost control

ABSTRACT

An electronic defrost system consisting of a circuit board designed to implement defrost cycle of an air source heat pump outdoor coil during the off-cycle period. off-cycle is when the house thermostat is satisfied, heat pump is timed off for two minutes and then reactivated in regular defrost cycle if defrost sensor is calling for defrost. (Temp/off cycle). When sensor opens, heat pump will shut off for two minutes to allow pressure equalization. 
     The automatic emergency heat is an option that can be selected. The automatic setting will activate the same circuit as the manual switch at the indoor house thermostat. 
     Defrost control board designed to activate all heat strips during defrost cycle if desired.

INCORPORATION BY REFERENCE

Title: Defrost system and method for heat pumps

Inventor: Shaw, David N.

Date: Mar. 10, 2009

Application Ser. No. 12/401,136

Specific reference: Paragraph [0002]-[0005]

The description goes into great detail how a heat pump defrost system operates.

SCHEMATIC AND CONNECTION LEGEND

-   12—Heat pump defrost control circuit board drawing -   13—Split unit connection drawing -   14—K-1 Defrost relay coil—24 volts -   16—K1-1 Energizes main contactor on heat pump -   18—K1-2 Energizes auxiliary heat during defrost cycle -   20—K1-3 Activates blower motor relay -   22—k1-4 Shifts reversing valve to cool mode for defrosting outdoor     coil -   24—K1-5 Interlocks K-2 during defrost cycle -   26—K1-6 Interlocks Y-2 -   28—K1-7 Energizes TD-4 -   30—K1-8 Prevents voltage feedback in running mode -   31—K1-9 Activates all heat strips -   32—K-2 Normal running mode coil—24 volts -   34—K2-1 Interlocks defrost coil K-1 -   36—K2-2 Interlocks K-3 to prevent K3-1 from opening during defrost     cycle -   37—K2-3 Energizes Y-1 in normal running mode (heat or cool) -   38—K-3 Emergency Heat relay coil—24 Volts -   40—K3-1 De energizes compressor and outdoor fan motor when emergency     heat activates automatically or manually -   42—K3-2 Prevents voltage feedback -   44—K-4 Outdoor fan motor relay coil—24 volts/10 amps -   46—K4-1 Stops outdoor fan motor during defrost cycle -   48—SW-1 Overrides K3-1 if heat strips are inoperable, or not     installed, enabling switch to run heat pump while automatic     emergency heat is on -   50—SW-2 Disables off cycle defrost -   52—SW-3 Disables automatic emergency heat -   54—SW-4 Disables thirty-minute defrost circuit. By placing switch     on, it will put secondary defrost circuit in thirty-minute time-on.     Place switch in off position for sixty-minute time-on -   55—SW-5 Selector switch for energizing all heat strip sequencers -   56—TD-1 Thirty-minutes on-make timer for automatic emergency heat.     Activates when House thermostat is approximately two degrees below     setting. -   58—TD-2 Two-minute on-make timer for pressure equalization -   60—TD-3 Thirty-minute on-make timer time/temp. secondary defrost     circuit -   62—TD-4 Two-minute off-timer reversing valve holding circuit for     pressure equalization -   64—TD-5 Three-second on-make timer resets TD-2 -   66—TD-6 Time delay-on two-minute timer. Holding circuit for pressure     equalization -   68—TD-7 Sixty-minute on-make defrost timer time/temp. secondary     circuit -   70—TD-8 Ten-minute off-break timer—terminates defrost cycle if     ambient temperature too cold for adequate defrost

Installation Instructions

-   72—NOTE: LVJB-Low voltage junction box -   74—G—Connect to green wire in LVJB -   76—Y-1 Connect to CC coil (main contactor on heat pump) -   78—Y-2 Connect series with yellow wire in LVJB -   80—O-R—24V—Connect parallel to red wire in LVJB -   82—O Reversing valve—Connect parallel to orange wire from house     thermostat in LVJB -   84—W1 Auxiliary heat—Connect parallel to white wire in LVJB -   86—E Emergency heat—Connect brown wire parallel in LVJB -   88—DFT Defrost sensor—Connect to DET on circuit board -   90—T1 Disconnect from defrosts relay N.C. contacts input side,     connect to T1 on defrost control board -   92—DR Defrost relay—Connect to DR N.C. contacts input side that     connects to outdoor fan motor. -   94—C Common—Connect parallel to blue wire in LVJB (blue on most     models)

FIELD OF INVENTION

This invention relates to the field of heat pumps, more particularly, this Invention presents a unique defrost method for air source heat pumps.

BACKGROUND OF THE INVENTION

There are patent applications that is referenced that describe an inherent problem with the prior art defrost system.

SUMMARY OF INVENTION

The present invention has timers incorporated so as to alleviate system shock by idling heat pump for a period of time and then initiate defrost cycle. At completion of defrost, it holds reversing valve in cool mode for a short time to allow pressure equalization.

The higher SEER rated heat pumps that has been mandated uses a higher pressure refrigerant which could wear more on the reversing valve on systems where the compressor continues to run during defrost cycle. Even a small blow-by leak can reduce the efficiency of a heat pump considerably.

Some heat pump manufacturers have designed their units with just the basic parts necessary. This gives the heat pump an increased reliability and less service call-outs. Switching to a defrost board that adds additional functions could be viewed as counter to what they have accomplished, but by utilizing the Off-Cycle Defrost System presented in the claims section, I believe it would increase reliability for the reversing valve and the entire system. A reversing valve is one of the more expensive repairs to make when leaks occur.

The biggest advantage to using the off-cycle system is it will have a clean coil on start-up, in addition, it is heating the entire time. It does the defrost after the thermostat has satisfied.

The automatic emergency heat circuit will save the homeowner from manually switching to emergency heat when temperature is too low to be efficient.

Supplemental heat stage one sequencer energizes when defrost initiated as in most prior art units. What's different about this system is the entire strip heat unit can be turned on during the entire defrost cycle if desired.

The circuit board as shown on the schematic is drafted with conventional parts for better understanding of the invention. The manufacturer will use logic circuits such as USASI, some magnetic relays, timers designed with hexadecimal counters. Microprocessor chips could also be used at the manufacturer's discretion.

The invention has been reduced to practice in the most basic form with board hard-wired (no etching), using relays and timers. No claim to an earlier filing date, only the provisional filing date is claimed.

Safety precautions will be printed for installers concerning using all heat strips with unit running during defrost without first checking breaker size, ampacity of conductors, also check register temperature if fibrous ducts installed. (max.125*)

To simulate defrost cycle when troubleshooting, unplug outdoor fan motor, check for 24 volts AC between DFT and common, turn thermostat down until heat pump shuts off.

The system that is presented is a basic modification from the prior art systems that is used in most heat pumps, but after reducing it to practice in a limited way, the present invention is much quieter during change-over, and it eliminates the sudden pressure/temperature change.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 consist of one off-cycle defrost schematic shown front view with all parts numbered and legends explained. This drawing is a simplified Formal Draft and is not the best mode. Reference paragraph [0009] for best mode.

FIG. 2 is a Connection diagram for split system heat pumps, illustrating that the connections are the same for split units as it is for a package unit.

OPERATION

The Off-Cycle Defrost Board will replace most existing PC boards in use, primarily the more basic boards used in residential package units and split systems.

The PCB will operate in heat or cool mode, defrost in off-cycle when temperature around forty degrees or below when system shuts down, either on normal off-cycle or forced off-cycle.

During defrost cycle a selector switch can activate all heat strips. (Optional)

In extremely cold weather the heat pump will automatically shut down and energize emergency heat which will be the same operation as manual emergency heat.

Description Of Prior Art

The reverse cycle Hot—Gas defrost system for heat pumps has been the preferred method by manufacturer's for many years. There has been many patents granted concerning defrost of heat pump coils that, for the most part, have been unsucessful for varying reasons. Many patents in the defrost field have been abandoned.

Prior Art References Follow:

A. Shaw, David N.

-   -   application Ser. No. 12/401,136     -   Filed: March 2009     -   Title: Defrost system and method for heat pumps

B. Maths, Derick A.

-   -   U.S. Pat. No. 5,332,028     -   Filed: July 1994     -   Ref: Claims 1-14

C. Shuster, Don A.

-   -   U.S. Pat. No. 5,758,507     -   Filed: June 1998     -   Title: Heat Pump Defrost control     -   Ref.: Abstract Background of Invention Summary

Reference US Class: 62/3; 62/81; 62/151; 62/259.1

Description of the Preferred Embodiment

Referring to the drawing FIG. 1, a schematic diagram is shown front view of an off-cycle heat pump defrost control 12 embodying the present invention with circuits to be etched and parts mounted on a PCB to be installed in the junction box of a package or split unit (outdoor condenser) with connections 74 through 94 made

In reference to connection diagram 13 FIG. 2 for split heat pump units, the defrost control board connections 13 are the same as the package units 12. The defrost board section 13 is the only relevant part to the present invention. 13 has the the same reference numbers as 12. The remainder of drawing 13 which includes the thermostat, air handler, and the outdoor low voltage junction box, is shown for Illustration purposes.

To further clarify the connections and the purpose of the circuits in FIGS. 1 and 2 referenced by identification numbers as follow:

-   G-74—Controls blower motor paralleled with existing green conductor     in LVJB 72. -   Y1-76—Connects to main contactor (CC) mounted inside heat pump and     controls outdoor fan and compressor. -   Y2-78—Connects series with yellow wire from house thermostat in LVJB     72. Conductor controls many functions on the defrost board to effect     defrost. -   R-80—24 Volts AC power source from secondary side of 240/24V     transformer. Connects parallel to red wire in LVJB 72 in heat pump. -   O-82—Reversing valve—Connects parallel to orange wire from house     thermostat in LVJB 72. Circuits will energize REV 82 when unit is     off and DFT 88 is calling for defrost. The valve 82 shifts to     cooling mode until defrost thermostat opens. -   W1-84—Auxiliary heat—Connects parallel to white wire in LVJB 72.     When unit goes into defrost, one stage of the heat strips 84 will be     energized unless SW-5/55 is closed during installation or by the     owner. Closed position will activate all heat strips 86 during     defrost cycle, including a two-minute time delay-on between     shut-down and defrost start-up 66. -   E-86—Emergency heat-Brown wire connects parallel in LVJB 72. EM HT     86 has two functions, one to furnish extra heat while in defrost, or     to shut down compressor and outdoor fan 76 automatically during     extremely cold weather when thermostat approximately two degrees     below balance—point for thirty minutes 56. Closing SW-3/52 will     activate EM HT 86 and is an option that the owner and installer can     choose. -   DFT-88—Defrost thermostat—Connects to defrost thermostat output side     to DFT 88 on circuit boards 12/13. DET t′stat is located on     refrigerant line to monitor for frost and ice build-up. DFT 88 is     the primary circuit that puts most other circuits in operation to     accomplish the defrost cycle. -   T1-90—Connects to T1 on CC (main contactor) located in heat pump and     feeds medium voltage to T1 terminal on circuit board. T1-90 runs the     outdoor fan through DR 92. K4-1 Normally closed contacts 46 opens     and will stop outdoor fan while in defrost mode. -   DR-92—Defrost relay contacts control OFM (outdoor fan motor) during     defrost cycle. These N.C. contacts could be eliminated if the     present invention is used. Connect DR 92 on defrost board to DR N.C.     contacts input side going to OFM. -   C-94—Common-Neutral side of the 24 volt AC power source 80. Connect     common to blue conductor (blue on most models) parallel in LVJB 72.

Since certain changes may be necessary in the foregoing disclosure without departing from the scope and spirit of the invention herein involved, it is intended that all matter contained in the above description and depicted in the accompanying schematic draft be construed in an illustrative way and not in a limiting sense. 

1. A defrost control apparatus designed to activate defrost cycle during off-cycle period, A. The circuit board is designed to defrost the outdoor coil every time the heat pump shuts down if defrost sensor is closed, This is a temp/off cycle mode, The unit will have a frost-free coil on start-up, B. Another board design function is if ambient temperature is too cold for house thermostat to satisfy, a selector switch set on 30/60 minutes will force the unit off on time/temp, and perform the same off-cycle defrost as the temp,/off cycle.
 2. An automatic emergency heat circuit will energize all heat strip relays or sequencers if balance-point stays approximately two degrees below indoor thermostat set-point for thirty minutes. Compressor and outdoor fan motor will be off during this time.
 3. As in prior art defrost cycles, the auxiliary heat (normally one heat strip) energizes. The present invention will give owner an option to energize all heat strips for entire defrost cycle, A. This will eliminate cold-blow for an acceptable temperature. 